1. Field of the Invention
This invention relates to the field of comminuting machines, such as the types employed for reducing demolition waste, land clearing debris, construction waste, trimmings, cuttings, and recyclables. The invention is directed more particularly toward an apparatus that employs a hammermill oriented along a horizontal axis of rotation with a horizontal in-feed of material, though the elements of the present invention can be practiced effectively in machines wherein the axis of rotation lies along an alternate plane, or in which the in-feed is of a different direction or orientation.
2. Description of Related Art
This invention relates specifically to a high-capacity horizontal-feed wood and debris shredding system, though it is to be understood that the invention is equally applicable to consumer grinders, mulchers, chippers, and other relatively low capacity waste reducers and recyclers. It is generally known in the art that horizontal feed mechanisms, such as conveyors or compression drives, can be utilized to feed material into a rapidly spinning "hammermill." A hammermill is essentially a drum, rotor, or series of plates substantially forming a cylinder, possessing teeth protruding from the outer surface of the drum, which teeth, ("cutting heads"), incrementally chop away the material being fed by the feed mechanism.
Such horizontal feed mechanisms are desirable because they allow for continuous, rather than batch, feeding of material to be comminuted. From the standpoint of effective and efficient comminuting, the in-feed should preferably deliver material to a horizontal hammermill in a manner that the hammermill will strike the material on the hammermill's downstroke. When material is struck by the downstroke of the hammermill, the material, while being struck, is momentarily wedged securely between the cutting head and the body of the apparatus, which houses the hammermill, resulting in a stable surface upon which the cutting heads of the hammermill can act. This stability allows substantially each stroke to impact the material in an optimum position, and each subsequent stroke to impact the material at the subsequent optimal position.
By contrast, when the in-feed delivers material to the hammermill at the up-stroke (i.e., "up-running hammermills"), the efficiency of the apparatus is significantly reduced. Because the upward rotation of the hammermill prevents the body of the apparatus from positioning and securing the material for a firm strike. Instead, the material tends to bounce away from the hammermill in response to the strike of the cutting heads. Elemental physics teaches that this results in an inefficient dissipation of the energy of the hammermill's strike. Furthermore, because of the bouncing effect, the subsequent strike point of the cutting heads on the material is a matter of chance. As a result, each strike is likely to be too shallow or too deep for efficiency.
Furthermore, the down-striking (i.e., "down-running") hammermill of the current invention maximizes safety, as material that is broken free by the hammermill is immediately directed downward and within the mechanism. Conventional `tub grinders` and up-running hammermills may throw material relatively long distances away from the mechanism, increasing the potential for bodily injury or property damage. This known tendency prevents recommended use of tub grinders in urban areas because of the distance objects potentially may be thrown. The users of tub grinders are accustomed to determining a "danger zone" in which thrown objects may land. A significant advantage of the hammermill of the current invention, however, is the reduced size of this "danger zone." The improved characteristics of the present invention create a smaller "danger zone" and under appropriate conditions and precautions potentially allow the use of the apparatus in urban areas and more populated spaces than tub grinders, with a greater expectation of safety in these areas.
Although the efficiency and safety of a down-running horizontal hammermill is recognized in the art, the application of the conventional construction of comminuting machines to such horizontal configurations has lead to unacceptable binding of material between the cutting heads and the body of the apparatus. The difficulties arise from relatively slender material of high compression strength, having lost contact with a restricting feed mechanism, entering the cutting area while oriented substantially parallel to the axis of rotation of the hammermill. When this occurs, the slender material can enter the hammermill cutting radius between the recessed portions of the cutting heads and the in-feed platform or the body of the apparatus. When this causes the material to exert pressure against a substantial length of the hammermill, of the hammermill may either jam or be damaged.
Numerous attempts in the art have been made to overcome the operational inefficiencies caused by binding jamming of hammermills. Some attempts have misidentified the problem, or at best, addressed relatively minor issues affecting performance of hammermills. A primary example is U.S. Pat. No. 5,628,467, issued to Graveman, which is primarily applied to up-running hammermills. Graveman identifies the problem with hammermill efficiency as caused by (1) windage, and (2) material becoming caught between cutting heads and rotating with the hammermill. To address these problems, Graveman teaches the use of "comb" fingers which extend into the circle defined by hammer elements, specifically, into the interstices between hammer elements. Graveman's combs fail to address the problem of material jamming between the hammers and the apparatus floor. Rather, they have the dual purpose of (1) raking out material from the hammermill which has become caught between adjacent hammers, and (2) preventing windage. In fact, Graveman initially places the comb at the outlet of the apparatus, rather than at the inlet. In such a configuration the combs cannot prevent material from being jammed between the hammer and the apparatus body.
Furthermore, while Graveman does supply an alternate embodiment employing combs at the inlet, the configuration taught still allows binding of the material against the housing, due to the placement and curvature of the housing. Additionally, the combs extend into interstices between all of the cutting heads regardless of length, which requires the comb teeth to be offset from the cutting heads; this arrangement necessitates a gap between each set of cutting heads that is large enough to allow clearance for the combs. This same clearance causes substantial material to remain uncut. Specifically, hardwoods and other resilient material will remain uncut at locations corresponding to the interstices between cutting heads. In real-world conditions, the material will take on a configuration similar to that of the comb, with fingers extending into the interstices. As the material is driven more deeply into the hammermill, the fingers of the material are forced against the shaft or other non-cutting elements of the hammermill, causing it to bind. The current invention, by contrast, orients shredders directly in line with shorter cutting heads, rather than maintaining some off-set from all cutting heads, as in Graveman. Also, the Graveman patent employs pivoting cutting heads, indicating that Graveman has not overcome the potential for binding addressed by the present invention. The orientation of the Graveman combs and the pivoting action of the cutting heads fails to address the dual problems of lengthwise entry of material and binding against the drive mechanism.
To avoid striking the comb elements that are positioned to remove major accumulation, Graveman discloses hammering elements of longer and shorter lengths. Graveman retains interstices between even the short and long hammers, and extends comb fingers into these interstices as well. These interstices produce the very drawback that the current invention seeks to address; namely, that fingers of hardwoods can protrude into the interstices and bind against the drive mechanism or shaft.
The wood-pulping industry has similarly attempted to maximize the efficiency of its shredders, though these shredders tend to rely upon finely sharpened cutting blades, as opposed to the more durable and robust hammermills of the present invention, which must be capable of operating under conditions that prevent maintenance of sharp blades. Nevertheless, examination of attempts in the wood-pulping industry is instructive, as it demonstrates further difficulties. U.S. Pat. No. 4,077,450, issued to Ackerman, discloses the use of "leading feet" (FIG. 6 and 3: 38-50). These leading feet operate as ramps which extend into the interstices between the main cutting elements, but not so far as to contact a shorter evening knife, which runs the length of the cutting drum. The main cutting elements cut a staggered pattern into the material, which staggering is then evened out by the evening knife. Initially, the ramps taught by Ackerman urge material into close contact with the barrel of the mill drum. This is necessary and desirable in pulping because the sharp blades are oriented to slice through thin slivers of material. Such a close arrangement in a true hammermill unacceptably promotes the frictional binding the art seeks to avoid.
Furthermore, the shorter evening knife of Ackerman does not prevent binding of the material against the mill. In fact, the evening knife exacerbates the difficulty with down-striking hammermills, because when an item of material enters the mill substantially parallel to its axis of rotation, the mill will bind if the blade is unable to overcome the resistive force of the material--the fact that Ackerman's evening knife runs the full length of the drum, extending to an identical distance above the drum at one point on the circumference causes the full length of the drum to meet the pressure of material at a single point in its rotation. The pressure accumulated at this single point is likely to overcome the motive force of the hammermill, causing jamming. As noted, a hammermill must be capable of operating while dull, which dullness makes jamming even likely in this configuration. Additionally, Ackerman is limited to situations that attempt to avoid lengthwise entry of material into the mill area. Ackerman is further limited to delicate situations in which the mill can possess sharp blades for cutting (such as the evening knife). Any attempt to run the Ackerman mill as a waste-reducer would rapidly dull the blades and cause significant jamming.
Similarly, Logan U.S. Pat. No. 3,219,076, discloses a pulping preparation shredder. While Logan teaches the use of staggered and shorter offset cutting surfaces, the reference further relies upon the need to have delicate, non-crushing blades that will not damage wood fibers. (1:14-36). Also, Logan indicates that it is important for cuts to be made parallel to the grain, as in Ackerman. These limitations significantly reduce the application of the Logan apparatus. Furthermore, Logan fails to realize that the unrestricted entry of material in a substantially parallel orientation to the hammermill is to be avoided.